1. Field of the Invention
The present invention relates to a paraquat resistance gene imparting paraquat resistance and a vascular tissue- and trichome-specific promoter.
2. Background Art
Plants are exposed to various environmental stresses on a regular basis including high and low temperatures, drought, high light intensity, salinity, air pollutant gases, pathogenic microbes and the like. Therefore, if useful plants that can grow sufficiently even under such types of environmental stresses such as, for example, crops, can be developed, food production will become possible even in regions in which crops and the like can not currently grow due to environmental stresses, and the possibility of being prepared for a grave food crisis that is forecast in the future will be increased. Consequently, the production of plants that have improved resistance to such kinds of environmental stresses is underway on a global basis. For example, plants have been produced that were imparted with chilling resistance (Nature, 356, 710-703, 1992; Plant Physiol., 105, 601-605, 1994), drought resistance (Plant Physiol., 107, 125-130, 1995; Nature, 379, 683-684, 1996; Nature Biotech., 17, 287-291, 1999), salt resistance (Science, 259, 508-510, 1993; Biotechnology, 14, 177-180, 1996; Plant J., 12, 133-142, 1997), air pollutants resistance (Plant Cell Physiol., 34, 129-135, 1993; Biotechnology, 12, 165-168, 1994), disease resistance (Kagaku to Seibutsu (Chemistry and Organisms), 37, 295-305, 385-392, 1999) and the like by genetic recombination techniques. Further, some plants that have been imparted with resistance to agricultural chemicals by genetic recombination techniques are in practical use (Nature, 317, 741-744, 1985; Proc. Natl. Acad. Sci. USA, 85, 391-395, 1988; EMBO J., 6, 2513-2518, 1987; EMBO J., 7, 1241-1248, 1988).
These environmental stresses are closely related with in vivo generation of active oxygen species (superoxide radical (O2−), hydrogen peroxide (H2O2), hydroxy radical (OH−)). Active oxygen species are generated by respiration, photosynthesis, environmental stresses and the like, and impart fatal damage to cells by excessive oxidation of proteins, nucleic acids, membrane structure or the like. It has also been reported that an active oxygen-resistant plant produced by genetic recombination techniques showed improved resistance to the aforementioned environmental stresses (Plant Physiol., 111, 1177-1181, 1996; FEBS Letters, 428, 47-51, 1998).
To produce an active oxygen-resistant plant, a method is principally employed in which a gene of enzyme scavenging active oxygen species (superoxide dismutase, ascorbate peroxidase, catalase and glutathione reductase and the like) is introduced into the plant.
Paraquat is a non-selective and potent herbicide that can kill all plants by continuously generating active oxygens in the photosystems. Paraquat resistance can thus be used as an indicator of the resistance to active oxygens, and analysis concerning the mechanism of paraquat resistance in plants has been conducted (Pestic. Biochem. Physiol., 26, 22-28, 1986; Theor. Appl. Genet. 75, 850-856, 1988; and Plant Physiol., 91, 1174-1178, 1989).
Meanwhile, an apoptosis suppressor gene (JP Patent Publications (Kokai) No. 10-309142; No. 2000-23583; and No. 2002-300822), a gene encoding a protein homologous to aldose reductase (JP Patent Publication (Kohyo) No. 2001-523466) and a gene encoding an iron-binding protein (ferritin) (JP Patent Publication (Kohyo) No. 2001-519671) have been disclosed as genes that can impart paraquat resistance. Further, in JP Patent Publications (Kokai) No. 2002-281979 and No. 2001-95585, peroxidase derived from paraquat resistant callus is disclosed as a gene capable of imparting resistance to paraquat.
It had been believed that if a paraquat resistance gene that can impart strong resistance to paraquat could be isolated, it would be useful in the development of plants with high resistance to active oxygens generated under various kinds of environmental stress conditions (high and low temperatures, drought, high light intensity, salinity, air pollutant gases, pathogenic microbes and the like). However, recently it has been revealed that active oxygens fulfill an important role as a molecule regulating the growth and stress response of a plant. Therefore, to avoid influencing important characteristics such as crop yield, it is important to increase the resistance of a plant to stresses such as paraquat without affecting the growth and physiological control mechanisms of a plant dependent on active oxygens.
The vascular tissue is a fascicular tissue system that differentiates through each organ of pteridophytes and spermatophytes, such as the stem, leaf and root. Xylem and phloem are the components of the vascular tissue, and they function as pipes to transport water and internal substances throughout the plant. Further, the vascular cambium, which includes the interfascicular cambium and the intrafascicular cambium, is found in the vascular tissue. The vascular cambium is a site of cell proliferation, and is thus an extremely important site for the growth of a plant. Thus, the vascular tissue is a location involved in transporting water and internal substances as well as cell proliferation in a plant. Accordingly, if a gene involved in transporting water or internal substances or in cell proliferation can be introduced into a plant and expressed specifically in the vascular tissue, it will be possible to regulate the transport of water or internal substances or cell proliferation in the plant.
In addition, from the viewpoint of plant diseases, the vascular tissue is a site where a wilt disease fungus infecting plants of the family Solanaceae proliferates and transfers. When a plant virus infects a plant, the plant virus migrates a long distance from one leaf to an above leaf, and therefore the vascular tissue is also a migration site that leads to systemic infection of a plant. Accordingly, if a gene involved in proliferation or migration of a fungus or plant virus can be introduced into a plant and expressed specifically in the vascular tissue, the plant can be protected from the fungus or plant virus.
A trichome is a floccose outgrowth found on the surface of a leaf, stem, sepal and the like of a plant body. A trichome is involved in secretion and excretion from the surface of a plant body. For example, it is reported that when a plant is exposed to heavy metal (cadmium) stress, the number of trichomes on the surface of leaves increases and crystals containing cadmium or calcium adhere to the surface of the leaves, in other words, that cadmium is excreted by a trichome (Planta, 213 (1), 45-50, 2001, May). A trichome is also the site of first contact for a filamentous fungus, bacterium, insect or the like invading a plant. Further, as a defense against diseases and insect damages, for example, a fluid having antimicrobial activity and a feeding deterrent effect is secreted from a glandular hair or glandular trichome of rugosa rose of the family Rosaceae, one type of trichome. Therefore, if a gene involved in the excretion of a heavy metal or the like, or a gene involved in the secretion of a fluid having antimicrobial activity or a feeding deterrent effect can be introduced into a plant and expressed specifically in a trichome, a heavy metal can be efficiently excreted from the plant or the plant can be effectively protected against a filamentous fungus, bacterium or insect invading the plant.
As described above, it is desirable that specific gene expression be performed in a vascular tissue or trichome. As a method for performing specific gene expression, a method involving the use of a promoter exhibiting specific promoter activity in a vascular tissue or trichome can be considered. However, a promoter exhibiting promoter activity specifically in both a vascular tissue and a trichome has not been identified at present.